2 questions about trolling motor wiring

[jspriddy]

While adding a circuit breaker (it had none) to my trolling motor today, I was checking various things and came across two things I have questions about:

One, while doing a continuity check on the hot circuit, I got a reading of 0.01 with the multimeter set on "20k", which I'm not certain what this means. Is this acceptable? I had to use a long lead due to the locations of the ends, but the lead isolated gave a reading of 0.00.

Out of curiosity, I then tested the ground at the foot control and got a reading of 1, which, since the motor runs, can't be right. I am not certain I was testing at the right terminal, tried them all, including one marked "common". Is it possible that the foot control is by-passed by the ground, and the ground goes straight to the motor itself?

I did the searches and came up with nothing.

Thanks,

 

[Barnacle_Bill]

Re: 2 questions about trolling motor wiring

All copper wire has resistance. The longer it is the higher the resistance and the smaller it is the higher the resistance. The higher resistance causes a higher voltage drop. That is why it is important to use the right size wire for the load at the end of it.

 

[jspriddy]

Re: 2 questions about trolling motor wiring

All copper wire has resistance. The longer it is the higher the resistance and the smaller it is the higher the resistance. The higher resistance causes a higher voltage drop. That is why it is important to use the right size wire for the load at the end of it.

But the question is, is this (0.01) an acceptable reading? Should I have been using a different setting on the multimeter?

 

[Silvertip]

Re: 2 questions about trolling motor wiring

1) Ground is not a factor with the switch. Ground is the return to the battery from the motor.
2) We have no idea what or how you were testing.
3) Rather than checking continuity, set the meter to read 12 volts (or 24 volts if you have a 24 volt system).
4) Measure voltage across the Positive and negative terminals at the trolling motor receptacle. If you have power, continuity is good. If not, THEN check continuity.
5) Set the meter on Rx1. Put the negative lead on the negative terminal of the battery. Note that I said the negative terminal of the battery - not the actual battery cable clamp. Put the other lead on the negative terminal in the receptacle. Any resistance reading will take into account the length of the wire, the resistance caused by the junction between the battery cable clamp, the length of wire you used to extend the test lead and any splices there may be in the the ground path. You do the same for the positive lead.
If you have power at the receptacle but the motor doesn't run, stop looking at the wiring. Concentrate on the motor.

 

[jspriddy]

Re: 2 questions about trolling motor wiring

1) Ground is not a factor with the switch. Ground is the return to the battery from the motor...

OK. So there is probably not a ground terminal in the foot control? What would the terminal in the foot control marked "common" be?

2) We have no idea what or how you were testing.

I was testing the continuity of the circuit to the trolling motor from the battery to the foot control since everything downstream seemed to be sealed. I tested the "hot" lead with a multimeter set to measure resistance, set to "20k". Maybe this is the wrong setting or even the wrong way to test continuity, but it seemed to me if resistance was 0, or slightly more, that would indicate that there was continuity.

The positive lead tested as described above gave a reading of "0.01", at the 20k setting. The ground lead was "1", if I had indeed found the ground in the control, which I don't think I had.

I was working with the battery disconnected and just checking things as I went. I'll connect it and do a voltage check.

5) Set the meter on Rx1...

I'm sorry, but my multimeter, being inexpensive, does not have a "Rx1". I've attached an image of one that's like mine.



Hope it helps to see what I was doing.

 

[dwparker99]

Re: 2 questions about trolling motor wiring

John,

When checking for continuity, you use the lowest resistance scale on the meter which in your case it looks like 20 ohms. But since you say your TM is running, why are you checking for continuity? What is the problem you are trying to solve?

 

[Silvertip]

Re: 2 questions about trolling motor wiring

It is nearly impossible to follow your desriptions of how you are testing and why you are testing.
Where ground goes once it leaves the batteries depends on where power goes into the troller. Sometimes the power cord enters the foot pedal and sometimes it enters the motor with a separate connection for the foot pedal. At this point we still don't know what brank and model motor you have or why you feel it necessary to check continuity.

So once again -- what is the problem?

 

[jspriddy]

Re: 2 questions about trolling motor wiring

It is nearly impossible to follow your desriptions of how you are testing and why you are testing.
Where ground goes once it leaves the batteries depends on where power goes into the troller. Sometimes the power cord enters the foot pedal and sometimes it enters the motor with a separate connection for the foot pedal. At this point we still don't know what brank and model motor you have or why you feel it necessary to check continuity.

So once again -- what is the problem?

John,

When checking for continuity, you use the lowest resistance scale on the meter which in your case it looks like 20 ohms. But since you say your TM is running, why are you checking for continuity? What is the problem you are trying to solve?

Again, I added a circuit breaker to the trolling motor (Minn Kota AT40) circuit. I had to extend the positive lead to the breaker, and then make up a lead on to the battery. Having looked in various catalogs, and could find no one offering to pay me to take a new trolling motor, I decided it would be prudent to check the continuity of the circuit after the above mentioned modifications.

With the multimeter set on "20k", I proceeded to "ohm" it, as a friend of mine who works on appliances puts it. With the multimeter set as previously described, I obtained a reading of "0.01". So once again, is this an acceptable result? Was my multimeter set correctly?

As for the ground, I'll just have to assume it bypasses the foot control, since I have no intent of taking it apart just to see. As I said earlier, this was a matter of curiosity, because I couldn't find the ground in the control unit.

"Han' me that roll of red NAPA war, Charlene, an' tah yo' end to the batt'ry". This sorta describes how my boat was wired when I got it. The boat, that is. I kinda wish I'd got Charlene instead.

 

[jspriddy]

Re: 2 questions about trolling motor wiring

OK.

Having studied the multimeter some, and deducing that "20k" means "20,000", which I should have seen right away, I determined that the resistance of the positive lead to the trolling motor was 200 ohms (20,000 x .01 = 200).

HERE'S the question: For a 40 amp trolling motor, IS this an acceptable figure? "To be or not to be" is NOT the question.

Many, many, many thanks,

John


SOME PEOPLE ARE LIKE SLINKIES - NOT REALLY GOOD FOR ANYTHING BUT THEY BRING A SMILE TO YOUR FACE WHEN PUSHED DOWN THE STAIRS.

UNKNOWN

 

[dwparker99]

Re: 2 questions about trolling motor wiring

OK.

Having studied the multimeter some, and deducing that "20k" means "20,000", which I should have seen right away, I determined that the resistance of the positive lead to the trolling motor was 200 ohms (20,000 x .01 = 200).

HERE'S the question: For a 40 amp trolling motor, IS this an acceptable figure? "To be or not to be" is NOT the question.

Many, many, many thanks,

John


SOME PEOPLE ARE LIKE SLINKIES - NOT REALLY GOOD FOR ANYTHING BUT THEY BRING A SMILE TO YOUR FACE WHEN PUSHED DOWN THE STAIRS.

UNKNOWN

200 ohms is not acceptable. You are not reading 200 ohms. With .01 displayed on the 20K scale means .01 ohms. This is not very accurate since the scale you used is so much higher than value displayed.

Not having continuity will not harm your TM. It would be like trying to operate with circuit breaker tripped.

What you should be concerned with is will the modifications carry the load? Did you use the proper size wire to extend/make-up the positive cable? Did you make good crimp/solder connections when installing terminal connectors?

Do a visual inspection on your work. Tug on the new connections. Briefly turn the TM on to see if prop rotates. Put the boat in the water, have a buddy operate on max while you feel each connection to make sure they are not getting hot. If all is well, go back ashore and pop a top on a brewski.

 

[Silvertip]

Re: 2 questions about trolling motor wiring

Still confused as to why you are so concerned about the "continuity". Connect the motor, put the rig in the water, turn it on, measure battery voltage. If it is anything above 12 volts (battery charged) you have continuity and are good to go. If the motor doesn't run you don't have continuity and are not good to go. If voltage drops below 12 you have a discharged battery or a battery that does not have enough capacity for the job. Only Minnkota knows what the resistance reading should be for their motors and that would depend on what speed you have selected. When using a digital meter to read resistance the display will show "1" open circuit. Short the two leads and the display will likely show ".001" or very close to it indicating closed circuit. Remember also that just because you are measuring resistance across the positive and negative motor leads you are not just measuring the continuity of the positive lead. Youa re measuring EVERYTHING in the circuit including the control board, foot pedal, the motor itself and any other circuitry in parallel with those two leads. Example: If you were to measure a 100 ohm resistor by itself the meter would display 100 ohms. If you placed another 100 ohm resistor in parallel with thefirst and now measured across them the reading would be 50 ohms. If you put them in series the resistance is 200 ohms. Sinice you have no idea what the circuitry is inside this foot control and the motor itself, you have no idea what is correct.

 

[jspriddy]

Re: 2 questions about trolling motor wiring

200 ohms is not acceptable. You are not reading 200 ohms. With .01 displayed on the 20K scale means .01 ohms. This is not very accurate since the scale you used is so much higher than value displayed.

Not having continuity will not harm your TM. It would be like trying to operate with circuit breaker tripped.

What you should be concerned with is will the modifications carry the load? Did you use the proper size wire to extend/make-up the positive cable? Did you make good crimp/solder connections when installing terminal connectors?

Do a visual inspection on your work. Tug on the new connections. Briefly turn the TM on to see if prop rotates. Put the boat in the water, have a buddy operate on max while you feel each connection to make sure they are not getting hot. If all is well, go back ashore and pop a top on a brewski.

So I should have used a lower scale, the 200, which is the lowest? I did use the proper material in adding to the circuit breaker, but I was concerned with the original part of the wiring that came with the boat. It's going on 18 years now and the wires to the TM are concealed. I have no way of knowing what previous owners may have done, considering some of the stuff I've found. And the last owner is supposed to be an electrician at a local industry.

I realize that if I had no continuity, the motor simply wouldn't run. The motor runs, but I didn't want to burn it out because the original wiring was bad and was not supplying ample current. I guess Silvertip's suggestion to check voltage at the motor was the correct test.

Thanks,

 

[jspriddy]

Re: 2 questions about trolling motor wiring

Still confused as to why you are so concerned about the "continuity". Connect the motor, put the rig in the water, turn it on, measure battery voltage. If it is anything above 12 volts (battery charged) you have continuity and are good to go. If the motor doesn't run you don't have continuity and are not good to go. If voltage drops below 12 you have a discharged battery or a battery that does not have enough capacity for the job. Only Minnkota knows what the resistance reading should be for their motors and that would depend on what speed you have selected. When using a digital meter to read resistance the display will show "1" open circuit. Short the two leads and the display will likely show ".001" or very close to it indicating closed circuit. Remember also that just because you are measuring resistance across the positive and negative motor leads you are not just measuring the continuity of the positive lead. Youa re measuring EVERYTHING in the circuit including the control board, foot pedal, the motor itself and any other circuitry in parallel with those two leads. Example: If you were to measure a 100 ohm resistor by itself the meter would display 100 ohms. If you placed another 100 ohm resistor in parallel with thefirst and now measured across them the reading would be 50 ohms. If you put them in series the resistance is 200 ohms. Sinice you have no idea what the circuitry is inside this foot control and the motor itself, you have no idea what is correct.

Let me put it this way-I wasn't so concerned as I was curious. My question was mainly theoretical. Every wire, circuit, component has some resistance by my understanding. What is an acceptable level of resistance? And, assuming the level was too high, would it damage something like a motor (as appliances are damaged by brown-outs)?

I was measuring continuity of the positive lead only by checking from one end, battery end, to where the lead came into the foot control. End to end on the positive lead only. As if I'd removed this wire completely and laid it on the floor to check. The circuitry inside the control was not involved.

I was trained on analog multimeters years ago while in generator school in Fort Belvoir, VA. But that's been so long it's all forgotten now. Would any component, i.e., wire, resistor, have to be isolated from everything to be tested accurately? I found this on another website:

An ohmmeter does not function with a circuit connected to a power supply. If you want to measure the resistance of a particular component, you must take it out of the circuit altogether and test it separately, as shown in diagram D:

"Diagram D" shows a resistor removed from its circuit and tested.

Thanks for your time,

 

[Silvertip]

Re: 2 questions about trolling motor wiring

I repeat -- you can measure resistance only if you are absolutely certain no other components are located between the two points you are measuring. You could measure it of course but if you don't know what's in between those two points you don't know if the measurement is acceptable or not. you are correct that even a length of wire has resistance. The longer it is the higher the resistance. Wire ampacity charts tell you what the resistance/foot is for various lengths of various size wire. Chances are you cannot measure accurately the resistance of a six foot piece of wire and besides, it is not of importance. If the wire isn't broken it is ok. You can prove whether it is broken or not by measuring the voltage at the source and at the destination. You can also use the voltage drop to mathematically calculate the resistance. If you want to know the resistance of a connection (ring terminal and screw, butt splice, or crimped ring terminal and screw, make a few connections and measure them. When you are done, what have you proved? You proved every connection has some resistance but in your applpication it is so small as to be a non-issue. One test of your system was all that was needed. Measure the voltage at the trolling motor receptacle. It is either present, it is low, or it is missing. In a 12 volt system the primary points of high resistance are the battery post/cable clamp inerface, ground connections, and splices. Ring terminal & screw connections or spade connections can cause issues but it usually the green corrosion that is the giveaway -- not a bunch a resistance checks. A good use of resistance checks are in ground paths because there is nothing between the device ground terminal and the negative terminal of the battery. Yes -- there may be a ground buss at the fuse panel or a single ground stud somewhere in the boat. If the bow light didn't work but it had power to it and bulb was good, check continuity between the exit point on the fixture and the negative terminal of the battery. If that circuit is open you don't have a ground. There oare other scenarios but on the hot side of a circuit a voltmeter is your friend. Use the ohmmeter to verify a bad switch, open bulb, non-functioning breaker -- and you would do that out of circuit.

 

[jspriddy]

Re: 2 questions about trolling motor wiring

I repeat -- you can measure resistance only if you are absolutely certain no other components are located between the two points you are measuring.... Use the ohmmeter to verify a bad switch, open bulb, non-functioning breaker -- and you would do that out of circuit.

Thanks. Now I understand why you kept questioning why I was checking for resistance, and why I shouldn't have been in this case.

Thanks again,

John

 

[Silvertip]

Re: 2 questions about trolling motor wiring

Thanks. Now I understand why you kept questioning why I was checking for resistance, and why I shouldn't have been in this case.

Thanks again,

John

I didn't mean to imply you "shouldn't" ever measure resistance. There are times when you need to. In this case I was just trying to determine why this was so important to you as on one hand it appeared there was a problem you were trying to diagnose and on the other it was a curiosity issue.

 

[jspriddy]

Re: 2 questions about trolling motor wiring

I didn't mean to imply you "shouldn't" ever measure resistance. There are times when you need to. In this case I was just trying to determine why this was so important to you as on one hand it appeared there was a problem you were trying to diagnose and on the other it was a curiosity issue.

Yeah. I meant I understand why measuring resistance was not the correct measurement in this instance.